C1pB is a member of a protein-disaggregating multi-chaperone system in Escherichia coli. Its three-dimensional structure and the mechanism of protein-folding activity mediated by C1pB is currently unknown. C1pB and several truncated constructs have been overexpressed and studied. We have received the expression system for the wild type C1pB and for a construct containing N-terminal 769 residues (out of 857), C1pBdeltaC. Crystallization efforts yielded crystals of ClpBdeltaC. The determination of the structure of these crystals using X-ray diffraction is the first, major objective of the proposal. It will be achieved either by the classical multiple isomorphous replacent method or by multiwavelength anomalous diffraction (MAD) of the selenomethionine form of the enzyme. These studies will be followed by ATP (or its non-hydrolyzable analogue) crystal binding studies. We will continue our efforts to crystallize the full length ClpB. If we are successful its structure will be determined using the molecular replacement method with the model of C1pBdeltaC. If we are not successful in crystallization, we will use homology modeling to obtain the structure of the missing C-terminal part. The structure of Hs1U (also known as C1pY) is avaliable and its residues 1-287 share 25% sequence identity with residues 551-857 of C1pB. There is no known structure of a protein homologous to the N-terminal 550 amino acids of ClpB.